基于氢氧同位素的洞庭湖枯水期蒸发研究

Study on evaporation of Dongting Lake during dry season based on hydrogen and oxygen isotopes

【目的】通过探讨洞庭湖枯水期不同水体的蒸发特征,揭示湖区水文循环规律,为湖区水资源管理提供参考。【方法】采用氢氧同位素示踪方法比较枯水期湖区河流、湖泊和地下水氢氧同位素组成及蒸发特征,并利用水量平衡方程和同位素质量守恒方程初步估算了湖水蒸发量。【结果】河水中湘江氧同位素千分偏差值δ_(^(18)O)和氢同位素千分偏差值δ_(D)平均值最大,松滋河的最小,沅江、资江和澧水的与湘江的差别不大;资水的氘过量参数d_(excess)平均值最大,松滋河的最小,其他河流的相差较小。河水、湖水、地下水的δ_(^(18)O)和δ_(D)变化范围分别为-10.66‰~-2.84‰和-76.27‰~-21.69‰、-6.59‰~-4.66‰和-40.65‰~-28.56‰、-8.33‰~-4.60‰和-57.12‰~-27.50‰。采用最小二乘法拟合的三类水体的蒸发线分别为δ_(D)=8.04δ_(^(18)O)+10.17,δ_(D)=5.02δ_(^(18)O)-6.58和δ_(D)=8.08δ_(^(18)O)+11.32。经比较认为,湖水蒸发作用最强烈,其次为河水蒸发作用和地下水蒸发作用,河水中蒸发作用强度由大到小依次为松滋河、城陵矶、沅江、湘江、澧水、资水。采用水量平衡法和同位素质量守恒法估算湖水枯水期蒸发量为0.173×10^(8)m^(3)/d,占湖水水量损失的4.1%。【结论】枯水期洞庭湖区不同水体、不同河流氢氧同位素组成和蒸发差异是水汽条件、地形和水文特征的差异所致,由蒸发导致的湖水水量损失较小。

[Purposes]By exploring the evaporation characteristics of different water bodies in Dongting Lake during the dry season,the hydrological cycle law of Dongting Lake was revealed,providing a reference for water resources management in Dongting Lake.[Methods]The hydrogen and oxygen isotope composition and evaporation characteristics of rivers,lakes,and underground water were compared by using the hydrogen and oxygen isotope tracer method,and the evaporation of the lake water was estimated by using water balance and isotope mass conservation equations.[Findings]The Xiangjiang River has the highest average values of oxygen isotope deviation valueδ_(^(18)O)and hydrogen isotope deviation valueδ_(D),and the Songzi River has the lowest values.The Yuanjiang River,Zijiang River,and Lishui River have little difference from Xiangjiang River.The average deuterium excess parameter d_(excess)of Zishui River is the largest,and that of the Songzi River is the smallest.Other rivers have little difference in terms of value.Theδ_(^(18)O)andδ_(D)range of river water,lake water,and underground water is[−10.66‰,−2.84‰]and[−76.27‰,−21.69‰],[−6.59‰,−4.66‰]and[−40.65‰,−28.56‰],[−8.33‰,−4.60‰]and[−57.12‰,−27.50‰].The evaporation lines of the three types of water bodies fitted by the least square method are as follows:δ_(D)=8.04δ18O+10.17,δ_(D)=5.02δ18O-6.58 andδ_(D)=8.08δ18O+11.32,respectively.It is believed that the evaporation of lake water is the strongest,followed by river water and underground water,and the evaporation intensity of river water in descending order is Songzi River,Chenglingji,Yuanjiang River,Xiangjiang River,Lishui River,and Zishui River.Water balance and isotope mass conservation methods are used to estimate the evaporation of the lake during the dry season as 0.173×10^(8)m^(3)/d,accounting for 4.1%of the water loss in the lake.[Conclusions]The difference of hydrogen and oxygen isotope composition and evaporation in different water bodies and rivers in Dongting Lake area during dry season is caused by the difference of water vapor conditions,topography and hydrological characteristics,and the water loss caused by evaporation is small.